For the first time, auditory research is being conducted on animals which are susceptible to atherosclerosis similar in pathology to that occurring in man. With a view towards potential elucidation of the pathophysiology of presbycusis as well as general modes of microcirculatory dysfunction in the body, White Carneau pigeons are being studied in age matched groups. First, sub-groups with normal diet and high cholesterol diet are being studied for potential blood-lipid rheology effects; next, sub-groups are being studied at intervals over two years as one group acquires diet-induced atherosclerosis. Pigeons with diet induced lesions will be taken off high cholesterol feeding at one year and studied for another year on a normal diet to test for possible "regression" effects. Pigeons are having correlative studies of A.C. cochlear potentials, serum cholesterol, aorta plaque area, aorta plaque cholesterol content, heart vessel cross-section study, celloidin cross-section and whole mount light microscopy of the inner ears, coagulation profiles and body organ histology.